Printing plate



Patented Nov. 24, 1942 PRINTING PLATE Clements Batcheller, Glens Falls,N. Y.

No Drawing. Application June 6, 1941, Serial No. 396,873

7 Claims. (Cl.'41-41.5)

larly to a new type of photo-lithographic printing .plate or masterhaving thereon a printing image of metal or metal oxides characterizedby its exceptional durability and long life.

The photo-lithographic processes now generally used for printing onpaper, metal, leather and the like involve the use of aphoto-lithographic plate of zinc or aluminum, certain portions of whichbearing the image to be printed are sensitive or receptive to printingink while the other, non-printing surfaces are insensitive to ink.Printing from such plates may be done either by the direct or offsetmethod. In the direct method the paper or other material is brought intocontact with the inked plate while in the offset method an inked imageis first transferred from the lithographic plate to a roller and thenceto the paper or other material as the roller is brought into contacttherewith.

In order to fix the image on the plate the surface of the plate is firstgrained and then coated with a light-sensitive composition usuallyconsisting of a solution of albumen or gelatine with a dichromate, anddried. The image is then formed in this light-sensitive coating byexposing it to the light of an electric are or other source of ultra'Xiolet light passing through a photographic nega- 've in contact withthe coating. The coating is tially soluble in water but those portionsthere- Qf which are exposed to the ultra violet light become insolubleor hardened. A so-called developing ink is applied to the plate afterthe exposure and the plate is developed by washing. The soluble portionsof the coating with the ink layer thereon are removed by the waterleaving only the insoluble portions with the superposed ink. In printingfrom such plates the non-printing areas are desensitized or madegreaseresisting so that they will attract and hold water and thus repelink.

The printing image on such plates obviously consists only of the film ofalbumen dichrornate and depends entirely for its integrity on theadherence of the film to the surface of the steel. Du to the structuralweakness of such an image it is easily damaged and the number of printedcopies that can be made therefrom is limited.

I have discovered a method of making a printing plate of this generaltype wherein the printing image is formed of metal or metal oxides whichare not only more resistant to damage than the ordinary albumendichromate films but which are more susceptible to ink than any albumenim- My invention relates to printing and particuwhich-are substantiallyindestructible when given ordinary care.

My plates are formed of alloy-steel containing at least 6%, by weight,of chromium, and preferably, containing chromium in such quantities (12%and up) as will render the steels substantially stainless. The presenceor absence of other elements in the alloy, such as copper, molybdenum,nickel, silicon and the other elements ordinarily used in stainlesssteels, is immaterial and any such elements may be present in thequantities usually encountered in steels of this character.

The plates are first grained by any of the wellknown processes and afilm of dark colored oxides is formed in and substantially integral withthe grained surface by treating the plate in a solution of sulphuricacid, water and a second acid selected from the group consisting ofchromic, vanadic, metavanadic, manganic and permanganic. However, Iprefer to use a solution of sulphuric acid, water and chromic acid whichmay be formed by adding any of the ehromates or dichromates, preferablysodium dichromate, to a solution of sulphuric acid and water. Thereaction, forms chromic acid and a sulfate or bisulfate of the chromateor dichromate-forming element. Small quantities of iron sulfate orchromium sulfate, or both, added to the solution facilitate thecoloring, and a solution which will show upon analysis the followingingredients within the proportions stated may be used:

Per cent by weight Water 35-55 Free sulphuric acid (1.84 sp. gr.) 15-55Chromic, vanadic, metavanadic; manganic or permanganic acid 2-120 Ironsulfate 0.01-10 Chromium sulfate 0.01-10 Other sulfates or bisulfatesand impurities Balance My preferred solution, in which the chromic acidis formed from sodium dichromate, will show upon analysis the followingingredients in about the proportions statedage, are capable ofreproducing finer details, and

Sodium sulfate or bisulfate and impurities Balance not of importance.

The solution is preferably heated to a temperature of about 180 to 220F. and the steel is simply immersed therein until a. film of darkcolored oxide is formed in and substantially integral with the grainedsurface of the steel. The time required varies quite widely with theanalysis of the steel and with the temperature of the solution. Withinthe preferred temperature range the coloring time, depending upon theanalysis and the passivity of the ball grained surface, may vary from 30minutes to 2 hours. The treatment should be continued until a darkcolored film is formed although the particular color is Blacks, blues,greens and maroons may appear.

It is to be understood that in commercial practice the printer wouldundoubtedly be supplied with grained plates colored as above describedand ready for his use.

Starting with such a pre-grained and pre-colored plate the coloredsurface of which is slightly porous and very sensitive to printing ink,the printing image may be imparted thereto either by ink transfer fromanother image or by printing it directly thereon from a negative orpositive in the same way that images are imparted to a Zinc or aluminumplate through the medium of a lightsensitive coating. For example, theimage may be printed in etching ink upon the colored plate in an offsetpress or by hand transfer, A resist of any suitable material is nextapplied to the image. As a resist, I prefer first to brush lightly overthe inked image a film of finely powdered asphalt and then to cover theasphalt with finely powdered French chalk. The powdered material adheresto the inked image but will not adhere to the other portions of theplate. The plate with the powdered asphalt and chalk thereon is thenheated to fuse or melt the asphalt into the ink image. No special degreeof heat is necessary except that it must be sufficient to fuse theasphalt.

Certain inks'such as high resin or varnish" inks, when dry, form asatisfactory resist in and of themselves, and where the image can beprinted in such inksno asphalt-chalk resist is necessary.

The plate with the resist covered image thereon is then subjected to anelectrolytic treatment which will strip off all of the exposed coloredoxides. This can be accomplished by treating the plate as anode inalmost any electrolyte which will not detrimentally affect either thesurface of the steel or the functioning of the resist. For example, ifit is desired to preserve-the grained surface of the steel inthenon-printing areas which is usually the case, the electrolyte shoudbe'such as will remove the color without injury to the graining. On theother hand, if the non-printing areas of the plate are to be etched to adepth below the level of the printing surface, then the electrolyte needonly be such as will not destroy the resist.

Examples of satisfactory electrolytes are as follows: a water solutioncontaining 10% nitric acid and 5% hydrochloric acid; a solution ofordinary household lye containing approximately 75 grams per liter ofwater; a solution containing 75 grams of sodium nitrate per liter ofwater;

a solution containing 70% phosphoric acid and 30% sulphuric acid with asmallquantity of citric acid dissolved therein; and 85% phosphoric acidsolution. Where a bath such as is used to color the steel isvonveniently available it may be used as an electrolyte to remove thecolored oxides. Electrolytes at room temperature work very well althoughhigher temperatures, provided they are not so high as to soften orremove the resist, may be employed, Violent evolution of gas from thesurface of the colored steel may remove the resist, particularly at theedges, and therefore the current density employed should be kept lowenough to avoid this. As a general rule it may be said that with mostelectrolytes a current density of about 1 ampere per sq. in. of film tobe removed will produce satisfactory results.

However, the proper current density and the duration of the treatment inany electrolyte can be easily determined by gradually increasing thecurrent until the surface (colored oxides) of the anode begin to growlight in color. Current is then permitted to flow at this amperage untilthe oxide film is removed or becomes easily removable by light rubbing.

After the removal of the colored oxides from the non-printing areas theresist and ink may be removed from the printing areas by any of thecommon solvents leaving the printing plate with the printing imagethereon consisting only of the colored oxides which are oxides orhydrated oxides of the alloying elements in the steel.

The plate is then ready for the printer and may be worked up on thepress in exactly the same manner as a plate bearing an albumen image.The colored oxides are very sensitive to ink and are capable of carryingmuch more rolled .on ink than the old type of albumen image.

Furthermore, the image, instead of being merely stuck on the steel as isthe case with an albumen image is actually in and substantially integralwith the steel itself.

It as clear, of course, that a plate made in this way must be consideredas a transfer plate because the image is produced by printing methodsfrom a plate already produced. There are, however, many occasions in theprinting industry where it is necessary to have several plates of thesame kind. As made by the usual methods, transfer plates can be used toproduce only a limited number of lithographic prints before the platestarts to break down. My transfer plates, however, are characterized byan exceptionally long i printing life because the ink sensitive image;which is formed entirely of oxides of iron, chromium, nickel and otheralloying elements in th steel is substantially indestructible whensubjected to ordinary care and normal use.

Where no plate is available from which a transfer can be made the imagemay be formed on my plate by the ordinary photographic methods now used.A light-sensitive film of albumen dichromate or other material, such asgelatine or asphalt, may be applied to my pre-grained and precoloredplate by the usual methods well understood in the art and the imageimparted to such film by means of printing from a photographic screennegative or positive, as may be required. Due to the porosity of theoxide color film the light hardened albumen image is anchored to theplate by being partially absorbed in the oxide film. A developing ink isapplied, rubbed down, and the plate developed by washing in the usualmanner which will of course remove the soluble albumen layer and thedeveloping ink from the non-printing areas leaving the insolubleimageforming albumen in the printing areas. The image is then inked upand a resist such as powdered asphalt and French chalk applied theretoand heat hardened as above described, or if a high resin or varnish inkis used, the ink itself, when dry, will form a satisfactory resist. Theplate may then be anodically treated as described above to remove thecolored oxides from the non-printing areas of the plate; the insolublealbumen with the overlying resist preventing the removal of the coloredoxides from the printing areas. Ihe resist can be then removed with asuitable solvent solution-of caustic soda although it may be permittedto wear off in use. In many types of printing which do not require theultimate in printed detail it is not necessary to remove the lighthardened albumen dichromate overlying the oxide image although for thefinest type of work superior results are attained by removing it becausethe oxide film on my plate is substantially more sensitive to thereception of lithographing ink than the albumen dichromate and, due toits exceptional durability will remain so throughout prolonged printingoperations.

Where it is desired to produce a deep-etched plate the light sensitivealbumen dichromate or other coating is hardened on the metal oxide layerin the non-printing areas. A developing ink is applied and the platedeveloped in the usual way. The plate may then be inked up with a highresin or varnish ink to form a resist or the resist may be formed frompowdered asphalt and French chalk, as described above, on surfaces whichhave been inked with ordinary lithographing ink. The oxide color on theexposed areas of the plate is then removed by an electrolytic treatment,as described above, and the plate etched by immersion in a normaltemperature solution of iron perchloride preferably of from 38 to 42Baum. By immersion for about 15 minutes in iron perchloride the exposedareas of the plate may be etched to a depth of about 3 thousandths of aninch which is considerably in excess of the depth to which plates of thepresent type can be deepetched. In order that the plate may be etcheduniformly the solution should be kept agitated by a current of air orother suitablemeans.

Where it is desired to produce a plate in which the printing areas arein relief above the nonprinting areas the resist is of course applied tothe printing areas, the color oxide stripped from the non-printing areaswhich are then etched in an iron perchloride solution, as abovedescribed.

In either case, the iron perchloride will produce on the stainless steela dull gray etched surface which is substantially the same color as thatof etched zinc but which is very susceptible to oxidation or rustingparticularly in the case of lowchrome alloy steels. In order torepassivate this surface and convert it to its original whiteness it maybe subjected to an electrolytic treatment as anode in an gredients setforth in the above formula used for coloring the steel. The electrolyteshould be used at normal atmospheric temperatures and the plate treatedfor about 1 minute with a current density of about 1 ampere per sq. ofsurface considering one side only of the anode.

While I prefer in the manufacture of deepetched or relief plates to useiron perchloride as an etching medium and thereafter to passify theetched surfaces by an electrolytic treatment as above described, it isto be understood that other etching media resist or tend to creep underthe edges thereof may be employed. For example, the etching may be doneelectrolytically by treating thesurface which do not injure the as anodein an electrolyte containing the same ingredients and in the sameproportions as is recommended for coloring the steel. Such treatment ata current density of from 1 to 2 amperes per sq. in. of surface to beetched will simultaneously etch and passify the steel. For such etching,however, I prefer to use an electrolyte formed by mixing- Parts byweight Water 900 330 Sulphuric aid (1.84 sp. gr)

Sodium dichromate -Q.

From the foregoing it will be apparent that my plate, except in thosecases where the albumen image is permitted to remain on the plate untilworn off, is substantially an integral structure consisting entirely ofmetal and metal oxides, and therefore has wear resisting properties farsuperior to metal plates upon which the printing image consists only ofan adhering film of albumen, gelatine or asphalt. Where such plates areused for printing directly upon metal or other particularly hardsurfaces as in the case of tin plate, etc. their resistance to wear isespecially advantageous. In addition, it will be found that much finerdetails may be accurately produced than is possible with any of thepresent types of albumen or gelatine coated plates.

What I claim is:

1. A printing plate formed of alloy steel containing at least 6%, byweight, of chromium and having printing and non-printing areas thereon,said printing areas comprising a colored film substantially integralwith said steel containing oxides of iron and chromium and forming theprinting image; the non-printing areas of said plate being substantiallyfree of said oxide film.

2. A photo-lithographic printing plate formed of chromium-containingalloy steel and having a photographic printing image substantiallyintegral therewith comprising oxides of the metals in said steel, andnon-printing areas on said plate substantially free of said oxides.

3. A photo-lithographic printing plate formed of chromium-containingalloy steel and having printing and non-printing areas thereon; saidprinting areas being in relief and comprising an ink-sensitive filmsubstantially integral with said plate containing oxides of the metalsin said steel and forming the printing image; said non-printing areasbeing substantially free of said oxide film.

4. A deep-etched photo-lithographic printing plate formed of achromium-containing alloy steel having printing and non-printing areasthereon; said non-printing areas comprising a film containing oxides ofthe metals in said steel plate having an ink-sensitive filmsubstantially integral with said surface formed of oxide of the metalsin said alloy, imparting the image to said light sensitive film,developing said plate, applying a resist to said image, and thereafterstripping said oxide film from the exposed portions of said plate.

6. Those steps in the method of making a photo-lithographic printingplate having ametalstrip said oxide film from the exposed portions 10 ofsaid plate.

'7. A photo-lithographic printing plate formed ofalloy steel containingchromium in a quantity at least suflicient to render said plate highlyresistant to corrosion, and having an ink-sensitive printing imagethereon comprising oxides of iron and chromium substantially integralwith said plate; the other portions of said plate being free of saidoxides.

CLEMENTS BATCHELLER.

